One of the applications of encased cylindrical filters is filtering lubricating oil in combustion motors so as to keep the oil free of impurities in operation. A second typical field of application for filters of this type is filtering hydraulic liquid in hydraulic systems. Since the filter is fouled in operation and has to be replaced at intervals, the filter casing must be removable from the device assembly to which it is attached.
There are previously known oil filters, in which the filter means and the surrounding casing have been constructed as a solid unit, replaceable as such. However, such a design is a waste of material ad also produces waste in abundance. From an ecological viewpoint, it is preferable to devise a casing that can be opened, so that the clogged filtering means alone is replaceable and the casing including a replacement means is put back in position in the device assembly. Patent application No. FI 955127 is cited as an example of such a design, in which the assembled oil filter described comprises a cylindrical, replaceable filter means, a perforated support pipe within the means, a collar as an extension of this pipe, a casing surrounding the means and a joint ring at the casing mouth. The collar has a thread, which connects the assembled filter with the device assembly, simultaneously providing a sealing between the joint ring and the device assembly.
In conventional filters of the type above, the casing must resist axial stress caused by the high pressure of the substance to be filtered, such as oil or hydraulic liquid, and for this reason the casing must be made of a rigid sheet material. The perforated support pipe must also be stiff enough to withstand the internal axial stress within the casing. However, the manufacture of such perforated pipes is awkward in terms of production techniques.
The purpose of this invention is to provide a filter with adequate resistance to the pressure within the filter casing caused by the substance to be filtered, and with the lower production costs than conventional filters. The filter in accordance with the invention is characterized by the fact that it includes a support member forming a solid extension of the collar, and consisting of an axial spindle inside the filter means and of an end flange at the end opposite to the collar, the periphery of the end flange being tightly sealed to the inner wall of the casing such that the support member will receive the internal pressure within the casing axially.